sourceMappingURL

This option allows you to automatically append the sourceMappingURL comment to the generated JS file.  Currently, an option to do this by default in Closure Compiler.

The generated comment will look something like this at the end of the JS file:

    //# sourceMappingURL=file.js.map

The sourceMapUrl option can be boolean true if you want to match the generated file's name or you can specify a string and name it whatever you'd like.
Don't see the point in this option, should just check for `options.create_source_map`